Adverse drug events among adult inpatients: a meta-analysis of observational studies

Studies in a number of countries have shown that adverse drug events (ADE) occur frequently among hospital inpatients. The objective of this study was to conduct a systematic review of observational studies of the frequency of ADE in adult inpatients and to examine factors associated with observed heterogeneity in the reported results.

The systematic review included observational studies, which identified and analysed ADE during hospitalization of adult inpatients. The literature search was conducted on MEDLINE, Embase, Lilacs and Google Scholar (January of 2000 to June of 2013). Article selection, quality assessment and information extraction were performed by two of the authors, working independently. Using the random-effects model, the proportion of patients with adverse events was used as an outcome measure. Proportion was estimated for subgroups based on event identification method: stimulated reporting (SR), retrospective monitoring (RM) and prospective monitoring (PM). For the latter group, meta-regression was used to identify sources of heterogeneity in the estimates.

Twenty-eight articles from the 7550 identified met our inclusion criteria. The articles were heterogeneous in terms of quality, outcome definition and event identification method and in the corresponding descriptions. Of the 28 articles selected, 25 were included in the corresponding quantitative summary: four used SR, six RM and 15 PM, returning incidences of 2·3% (CI 95%: 1·6-4·5), 8·7% (CI 95%: 4·8-15·3) and 21·3% (CI 95%: 15·7-28·3), respectively, and I(2) greater than 95%. There were other sources of heterogeneity, including the use of combined strategies within each subgroup. In the PM subgroup, using multivariate meta-regression model, no variables were found to associate with proportion.

Event frequency seems to associate with the event identification method. PM returned the highest estimates. This subgroup used a greater diversity of approaches for event identification and more diverse data sources. Improved recording of information on the event identification method, the characteristics of the events and the conduct of the study would enable more reliable and precise estimates of the frequency of ADE among hospital inpatients.